GAS/LPG ENGINE LINE PRESSURE

[CINVJGG]

Hi,

I am running a gas engine with LPG. It works fine unitl I run it on full load. At that moment knocking begins and it shuts down. I have the feeling that the fuel line from the tank to the engine is not fine (there are way too many accesories). However gas line pressure is stable. Would it be possible to have stable pressure at different loads but not enough gas in the line for high loads?

 

[catserveng]

Pretty easy to determine if you have enough fuel supply. If this is a carburated engine, then measuring fuel differential pressure to the carb fuel inlet is a good start.

The "knocking" you describe is usually detonation.

You haven't provided much in the way of details on your engine, application and environment, all which can affect engine performance. Some additional info from you will likely get you a better answer.

MikeL.

 

[CINVJGG]

Thanks MikeL.

The application is a generator set (about 400KW). The unit has two regulators: first one reduces pressure from 1 bar to 40mbar. The second one reduces pressure to zero.

Before the genset (fuel line) is a pressure regulator (15psi). On this (line regulator) pressure is constant during our tests (load bank). Up until about 70% of load, the unit runs fine. With higher loads the genset begins detonating. We are considering the fuel flow to be insufficient. However, we are not sure if having a constant fuel pressure in the line regulator means that there is not lack of flow or if it is possible to have insufficient flow while keeping the line pressure constant.

BTW, there is no carburator. It goes like this: line, 40mbar regulator, zero pressure regulator, mixer, turbo, aftercooler, throttle valve.

Thanks for your help.

 

[catserveng]

Normally when a low gas pressure type engine has a fuel supply problem, throttle goes wide open and engine either gets unstable or drops RPM. If you have a detonation issue, and your ignition timing is as defined by the manufacturer for the fuel being used, then you may have a fuel mixture issue.

You state this has been an issue while testing on a load bank. what other symptoms are present when the detonation starts to occur? does the speed fluctuate or drop? Is the unit equipped with a knock detection system that changes timing and/or shuts the unit down when knock exceeds a set limit?

How do you verify proper fuel mixture? Do you use an emissions analyzer, or is there an onboard air/fuel ratio control?

Is this a problem on a unit that had performed properly in the past and this is a recent problem, or is it a problem since start-up?

Have you gone thru the tuning and adjustment procedures as defined by the manufacturer of the engine?

In that size range lots of ways engines get controlled. In my experience detonation and low fuel supply pressure usually are not related in most SI industrial engines.

MikeL.

 

[LadaTrouble]

Do you have heating for the regulators ? Working hard they will freeze up without hot water plumbed to them.

 

[Danandersen]

I've had similar issues on a few Waukeshas - In most cases it was faulty plugs. IMHO the pressure was too great for the plugs to overcome so the ignition of the
air and fuel was not properly timed.
Or too high charge air temperature causing pre-detonation.

As catserveng says, your throttle should move to wide open and you would most likely also see an Increase in Intake Manifold Pressure.


Any number of things could cause a knocks and loss of power. Could you describe the problem a little more?

 

[gruntguru]

You could have an Octane Number problem. Even the best LPG (straight propane) has a lower octane rating than methane. LPG is often a propane-butane mix. The more butane the lower the octane.

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